# returns from to date informations of given group member

getGroupMember <- function(groupdf, membercode) {
  for (i in 1:dim(groupdf)[1]) {
    if (groupdf[i,"code"] == membercode) {
      return (c(groupdf[i,"from"], groupdf[i,"to"]))
    }
  }
  print("Error: membercode in group data.frame not found")
  return (FALSE)
}